Plain carbon steel and low alloys used in corrosive environments can be susceptible to corrosion by the reduction or oxidation process because the naturally occurring protective oxide layer is not sufficient to maintain stability. Even the higher alloys such as nickel-, cobalt-, and titanium-base alloys exhibit limits in certain environments. There are many methods to modify the surface of carbon steels and low alloys by aluminizing the surface with thermal spray of aluminum or a higher alloy such as austenitic stainless steel. Thermal sprays in some cases provide the necessary protection and life extension designed into the part, as is described in detail in the American Welding Society report AWS C2.14-74. "Corrosion Tests of Flame-Sprayed Coated Steel, 19-Year Report." However, thermal sprays are only coatings mechanically bonded to the surface and can be removed by permeation of corrosion gases, thus separating the coating from the base material. Another form of failure which thermal sprayed coatings undergo is differential thermal expansion between the base material and the coating.
CVD (chemical vapor deposition) and PVD (physical vapor deposition) are delivery systems that can transfer corrosion resistant metal vapors to the surface of the base material. CVD and PVD both are limited to smaller processing sizes and cost effective logistics. There is a need for a method that allows for large surface areas to be thermally sprayed with a diffusable corrosion resistant metal without disbonding of the thermally sprayed coating or melting and run-off of the thermally sprayed coating. The method should provide for use of a cost effective iron-, nickel-, cobalt-, or titanium-base material with a corrosion resistant alloy surface.
The method should not be limited to flat components, but be useful to treat angular and rounded parts, irrespective to part geometry that can be thermally sprayed.